1. Field
The present invention relates to a printed circuit board having metal bumps and a method of manufacturing the same, and more particularly to a printed circuit board having metal bumps which have even heights and make direct connections with a circuit pattern without using additional bump pads thus allowing the arrangement thereof at fine pitches, and a method of manufacturing the same.
2. Description of the Related Art
With the recent advancement of the electronics industry, electronic components are being developed to have high performance and thus there is a demand for miniaturized and highly-densified packages. Accordingly, interposers (substrates) which functions to connect ICs to a main board must be packed more densely. The high densification of packages is attributable to an increase of the number of I/Os of ICs, and the method for the connection with the interposers has also been made more efficient. As methods of mounting ICs on a board to manufacture a high density package, a wire bonding process or a flip bonding process are currently used. In this regard, as the number of I/Os is increased above a certain number, the flip chip process is preferably used because of an increase in the manufacturing costs.
FIGS. 1A to 1E are cross-sectional views showing a conventional process of manufacturing an outermost layer of a printed circuit board on which semiconductor chips are mounted.
As shown in FIG. 1A, a solder resist 15 is formed on a substrate 11 having pads 13. The solder resist 15 is positioned between the pads 13 so as to prevent solder paste 19 from flowing down and spreading out and over during the subsequent formation of bumps 23.
Thereafter, as shown in FIG. 1B, a print mask 17 is placed on the solder resist 15. At this point, the print mask 17 functions to block application of the solder paste onto the solder resist 15 and to enable the solder paste applied on the pads 13 to be of a predetermined height.
As shown in FIG. 1C, the pads 13 are printed with the solder paste 19 using a squeegee blade 21. Consequently, the solder paste 19 is charged in recesses defined by the solder resist 15 and the print mask 17.
As shown in FIG. 1D, the print mask 17 is removed from the solder resist 15. Subsequently, as shown in FIG. 1E, a reflow process is conducted, with the result that a printed circuit board having bumps 23 is manufactured.
However, the above-described conventional process of forming bumps of a printed circuit board using a printing technique is disadvantageous in that it is hard to realize bumps arranged at pitches of 120 μm or less. Accordingly, when bumps are formed at fine pitches using the printing technique, the bumps are abnormally shaped. Furthermore, even if the bumps are normally shaped, the volume of the bumps is excessively decreased.
In addition, since the pads 13 are formed using a plating technique, uneven thickness of the pads may occur because of inherent errors in the plating. Furthermore, since it is hard to evenly distribute the amount of solder paste used when printing it during the printing process, uneven heights of bumps 23 result so that bumps 23 which are not connected to a semiconductor chip may occur.
In addition, because the height difference between the solder resist and the pads 13 is considerably increased, there is a problem in that voids occur during an underfill process subsequent to the mounting of electronic components.